1. Field of the Invention:
This invention relates to the manufacture of 2,4-hexadiyne-1,6-diol.
2. Disussion of the Background:
2,4-Hexadiyne-1,6-diol may be prepared by hydroxymethylation of diacetylene with formaldehyde. However because of the hazardous nature of diacetylene which has a tendency to decompose explosively, it is recommended that this compound be employed only at high dilution. Consequently, it is difficult to devise an economically feasible process for making 2,4-hexadiyne-1,6-diol by using this approach.
2,4-Hexadiyne-1,6-diol may also be prepared, quite safely, from propargyl alcohol, by oxidative coupling via the Glaser method A suitable process is described in Brandsma, L., 1971, "Preparative acetylenic chemistry", pub. Elsevier, Amsterdam, p. 166.
The disadvantage of this process is that 2,4-hexadiyne-1,6-diol, being relatively insoluble, precipitates out of the reaction mixture and the crystal-containing slurry obtained by this process is costly to refine. In addition, the slurry contains salts of the catalyst for the oxidative coupling of the propargyl alcohol. These salts have to be separated from the product, but because 2,4-hexadiyne-1,6-diol is slightly water-soluble, water washing results in product loss. Separation by distillation is also unsuitable, because 2,4-hexadiyne-1,6-diol is heat-labile; under a vacuum it boils at a higher temperature than water.
The well known ion exchange technique is suitable for recovering the salts from the product if the salt content is not too high. However, when the ion exchanger is regenerated, salt-containing eluates are released, which represent not only loss of product but also an environmental contamination problem.
Use of reverse osmosis for desalination is not an option, because there are problems with the stability of the membranes and with the permeate stream in organic media. And the salt-containing retentate also needs to be further processed.
There is thus a need for a process which permits the economical and safe preparation of 2,4-hexadiyne-1,6-diol, where the salts are removed from the product, where the salts do not cause an environmental problem, and where the 2,4-hexadiyne-1,6-diol product does not crystallize out of the reaction mixture.